This problem shows its ugly head on Canvas Apps, be they standalone, or Sharepoint custom forms.
My focus currently is in customizing Sharepoint Forms with PA. If you try to do some minimum customization, such as e.g.
SET() to attribute a variable based from a value on the loaded data on the form, it may not set it correctly the first time the custom form is loaded.
Clicking on a second item on the sharepoint list has the second item load correctly.
Clicking again on the first item then loads it correctly.
This makes it problematic to do relatively modest changes like e.g. Conditionally load a custom set of item on a select box, based on an existing value. The above behavior is prone to user error and inconsistent form behavior leading to other problems.
Besides the error-prone clickfest above, a workaround to it is a fugly kludge: subvert the initial editForm with a read-only display, and create a second view with an actual, editForm, which can be accessed by clicking on a button in the default view.
This requires a lot of additional setup and needless complexity, and significantly raises the bar from the proposed "codelesss app platform", becoming much more difficult for newcomers.